Powder coating compositions are regarded attractive as low-pollution paint because no organic solvents volatilize into the atmosphere during coating operation. In particular, polyester resin based powder coating compositions comprising a polyester resin and a crosslinker are known applicable to metal articles. As the crosslinker used therein, triglycidyl isocyanurate (TGIC) and blocked polyisocyanates are well known. The use of TGIC is undesirable because of its skin irritation and toxicity. The blocked polyisocyanates have the problems that the blocking agents are substances regulated by the Pollutant Release and Transfer Register (PRTR), and blocked polyisocyanates become volatile organic compounds (VOC) if released during bake of a coating.
From the environmental aspect, attention is paid to hydroxyalkylamide compounds, which are curing agents free of blocking agents. For example, JP-A H05-156178 and JP-A H10-017660 disclose powder coating compositions comprising hydroxyalkylamide compounds. However, polyester resin-based powder coating compositions using hydroxyalkylamide compounds as the curing agent are less adhesive, failing to form coatings having satisfactory water-loading resistant performance.